Shear Strength of Continuous Lightly Reinforced T-Beams

Abstract

The shear strength of continuous lightly reinforced concrete T -beams is studied. Six twospan T -beams with and without web reinforcement are tested. The primary variables are longitudinal reinforcement ratio (0.75% and 1.0%) and nominal stirrup strength (0 to 82 psi). The test results are analyzed and compared with the shear design provisions of "Building Code Requirements for Reinforced Concrete (ACI 318-89)" and predictions of other investigators, including predictions obtained using the modified compression field theory. The tests indicate that ACI 318-89 overpredicts the concrete shear capacity of lightly reinforced beams without shear reinforcement. Little difference exists between shear cracking stresses in the negative and positive moment regions for beams in the current study. For both the negative and positive moment regions, the stirrup contribution to shear strength exceeds the value predicted by ACI 318-89. Stirrup contribution to shear strength increases with increasing flexural reinforcement ratio. Overall, the ACI 318-89 shear provisions are conservative for the beams tested in the current study. Two procedures based on the modified compression field theory are also conservative. ACI 318-89 better predicts the nominal shear strength of the beams in the current study than either of the modified compression field theory procedures.